Gem spinels were first discovered in Luc Yen (Yen Bai province) in 1985, together with ruby and sapphire in placers. Spinels from Luc Yen can be seen in different colors: red, pink, purple, sea blue and sky blue. Gem quality spinels have been found and exploited in placers, meanwhile spinels in host rocks (white marble) are usually of low quality and are used mainly as sample collections. The color of Luc Yen spinel changes depending on the concentration of impurity elements. The presence of chromium (Cr2O3) gives red and pink color, the combination of Cr2O3 and FeO gives purple color. Cobalt (CoO) gives blue color. Iron ( Fe2O3) causes brown shade and brownish luster. .. An inclusion assemblage has been discovered, consisting of apatite, goethite, rutile, orthoclase and negative crystals.